High-voltage (HV) transistors are broadly utilized as switches in power supplies (e.g., AC/DC converters) for industrial and consumer electronics. In such applications, input voltages may be very high, for example from 500V to 1000V. Thus, high-voltage transistors need to have high breakdown voltages to withstand such high input voltages.
Many high-voltage transistors are designed as vertical transistors in which a direction of current flow is into a semiconductor substrate (i.e., perpendicular to a surface of the semiconductor substrate). Such a configuration may provide a small on-resistance for a given breakdown voltage and better power handling capability. Yet, many high-voltage semiconductor transistors are also designed as “lateral” transistors (i.e., a current flow is parallel with the surface of the semiconductor substrate) because lateral HV transistors can usually be fabricated with processes generally similar to those used for low-voltage (LV) devices, allowing integration of HV and LV devices to provide “integrated power” functionality.
One limitation of conventional lateral high-voltage transistors is the inability to handle high avalanche currents due, for example, to localized breakdown usually where electric fields are highest. This weakness limits the ability of lateral HV transistors to protect themselves during over-voltage conditions. Accordingly, there is a need for devices with HV transistors and integrated over-voltage protection circuits to provide improved immunity to damage during over-voltage conditions.